Mechanism Of Phase Behavior For Systems Based On Ionic Liquid And Poly(N-isopropylacrylamide)

This work is concentrating on discussing mechanism of phase behavior for systems based on ionic liquid and poly(N-isopropylacrylamide). FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and perturbation correlation moving window (PCMW) technique is utilized to discuss the mechanism Mainly, the microdynamics of the phase transition and the influence of ionic liquid are investigated:the interaction among polymer, cations and anions, in particular the variation of the ion environment in ionic liquid; the model of interaction between ionic liquid and PNIPAM solutions under the variation of ionic liquid concentration; and the influence of introduction of poly(BVImBr) segment on solution properties of the block polymer. This fundamental study can provide theoretical background for the application of ionic liquid-polymer systems.The whole paper is composed of five chapters.An introduction of the entire work is provided in Chapter I, Herein, a brief introduction on the chemical structure and property of ionic liquid and poly(N-isopropylacrylamide) is offered. The process of research on the phase behavior for systems based on ionic liquid and poly(N-isopropylacrylamide) are well recommended. Besides, detailed information about2Dcos and PCMW is attached, acting as a background for understanding the investigation methods in the following researchs.In Chapter II, the gelation microdynamic mechanism of PNIPAM in a ionic liquid,1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) is investigated by FTIR spectroscopy in combination with2Dcos and PCMW for the first time. Appreciable changes in band frequencies and shapes can be observed for the v(N-H) and v(C=O) regions, indicating the formation of new interaction between the ionic liquids and PNIPAM and the transformation of interior interaction between polymer chains during gelation. In the v(C-H) region of imidazole ring, though slight changes can be noted in1DIR, the region is valued for the investigation on the ion environment.2Dcos results suggest the variation of the ion environment take place with the relative change of the isolated (free ions or smaller ion pairs) and associated (larger ion clusters) components of [C2mim][NTf2]. The construction of associated species related to solvation in ILs, is the possible driving force on the sol-to-gel transition of PNIPAM.The microdynamic mechanism during gelation is given. Upon cooling, following the change of ion environment, the side chains of PNIPAM experience a changing process from dissociation of the interaction with ionic liquid to formation of N-H…O=C hydrogen bonding, where the C=O groups get rid of the weaker hydrogen bonds via C4.5-H earlier than that via C2-H. Moreover, the motion of side chains occurs before that of the PNIPAM backbone, leading to the shrinkage of polymer from the side chains to backbone together with forming the polymer network. Finally, the immobilization of the associated species in the polymer chains network results in the opaque gel formation, which meanwhile, is actually a desolvation process upon the variation of ion environment.In Chapter III, the role of [Bmim][BF4] dynamics on transition behavior of concentrated PNIPAM solutions is elucidated and the model of interaction between ionic liquid and PNIPAM solutions under the variation of ionic liquid concentration is given. The addition of IL is interesting because it modifies phase transition behavior of the PNIPAM aqueous solution:at low IL concentration, the Tp of PNIPAM solution shifts down with the IL increase, due to the destabilization of the hydrated macromolecule structure; however, at higher IL concentration, unexpectedly, the phase transition behavior disappears, attributed to the formation of stable interaction network via intra-and intermolecular hydrogen bonding, such as the intermolecular hydrogen bonds of C=O…D-N at the low temperature, resulting from the hydrophobic collapse caused by the IL, not the response to the thermal perturbation.As temperature elevates, the sample with0.4mol/L IL shows two change steps during the phase transition:in the former step, IL molecules damage the hydration effect of the C-H groups via H-bonded with water molecules preferentially; in the latter, IL-D2O association takes part in the globule construction, probably via the interaction with hydrophilic groups of PNIPAM (C=O groups). Thus, the role of IL dynamics on the phase behavior is mainly embodied in two opposite aspects, which, meanwhile, the "destroyer", as well as the "constructer".In Chapter IV, the assembly properties, thermal phase behavior and microdynamics of poly(NIPAM-b-BVImBr) in aqueous solution are investigated. Particularly, three influence of introduction of poly(BVImBr) segment on solution properties of the block polymer are concluded:the formation of core-shell micelle structure, the higher LCST, and the stronger hysteresis in aqueous solution.By introduction of Poly(BVImBr) segment, poly(NIPAM-b-BVImBr) is regarded as the micelles consisting of a relatively hydrophobic core of poly(BVImBr) and a hydrophilic shell of PNIPAM in aqueous solution. Compared with PNIPAM solution, poly(NIPAM-b-BVImBr) aqueous solution shows an increase in phase transition temperature, as the result of one more step dehydration process originated from the side alkyl chains PIL segment.Interestingly, by the calculation of component variation of carbonyl hydrogen bonds, we found that the C=O groups form hydrogen bonds with the N-D groups at the original state, due to the accessible environment of micelle structure, which is regarded as the intra-micelle hydrogen bonding; when the temperature elevates above LCST, the hydrogen bonds of C=O…D-N among aggregation of micelles take place, which is called inter-micelle hydrogen bonding.What’s more, the stronger hysteresis of poly(NIPAM-b-BVImBr) aqeuous solution is closely related to the different microdynamics during heating and cooling: when temperature elevates, the remaining C=O groups form new hydrogen bonds with remaining N-D groups of intra-micelle preferentially, accompanying with the PNIPAM chain aggregation and collapse on the shell of micelle, then followed by the inter-micelle hydrogen bonds of C=O-D-N, leading to the final aggregation of micelles; however, in the recovery process, the strong C=O…D-N among micelles aggregation (including C=O-D-N intra-and inter-interaction during heating) formed during heating is harder to remove, but also, the reconstruction of C=O…D-O-D and the recovery hydration process for C-H groups are prevented due to the compact and regular core-shell strucures.Chapter V shows a conclusion of the whole work. Mainly, FTIR spectroscopy in combination with2Dcos and PCMW is utilized to discuss the microdynamic mechanism of phase behavior for systems based on ionic liquid and poly(N-isopropylacrylamide). The significance of this study is to provide theoretical background for the application and further study of ionic liquid-polymer systems.